Continuous small diameter ferrous tube manufacture

ABSTRACT

A PROCESS AND APPARATUS FOR THE PRODUCTION OF ANNEALED STAINLESS STEEL TUBING IN ONE CONINUOUS OPERATION IS DISCLOSED. RESISTANCE HEATING OF THE TUBE IS EMPLOYED THROUGH CURRENT APPLIED BY GRAPHITE BRUSHES. A QUENCHING STEP IS ACHIEVED BEFORE THE ADVANCING TUBE CONTACTS THE SECOND BRUSH SET. THE QUENCHING DEVICE, BRUSH CONFIGURATION AND STRESS-LIMITING ADVANCEMENT OF THE TUBE CONTINUOUSLY WITHOUT BUCKLING OR UNDUE STRETCHING ARE DESCRIBED. APPARATUS FOR PRACTISING THE PROCESS WITH BRIGHT ANNEALING IS DISCLOSED WHICH INVOLVES MAINTAINING AN ENVELOPE OF INERT GAS AROUND THE RESISTANCE HEATING STAGE.

12 Sheets-Sheet 1 INVENTOR GLENN J. GIBSON w 85 85 m HEEEEEW 3 I 8m 335%: 558 021522? 5 mm 5%? 02:52.2

G. J. GIBSON CONTINUOUS SMALL DIAMETER FERROUS TUBE MANUFACTURE Feb. 9,1971 Filed March 29, 1968 6- J. GIBSON Feb. 9, 1911 CONTINUOUS SMALLDIAMETER FERROUS TUBE MANUFACTURE Filed March 29. 1968 2 Sheets-Sheet 2FIG. .5

United States Patent O 3,562,031 CONTINUOUS SMALL DIAMETER FERROUS TUBEMANUFACTURE Glenn J. Gibson, 97 Beech Ave., Berkeley Heights, NJ. 07922Filed Mar. 29, 1968, Ser. No. 717,273 Int. Cl. C21d 9/08 US. Cl. 148-1546 Claims ABSTRACT OF THE DISCLOSURE FIELD OF THE INVENTION Thisinvention relates to the manufacture of metal tubing and moreparticularly concerns a process and apparatus for the continuousproduction of annealed tubing.

BACKGROUND OF THE INVENTION The manufacture of annealed tubing atpresent typically involves feeding metal strip from a reel through atube forming mill and then through a welding step where the edges arejoined and the tubing cut to length. Annealing is then performed as aseparate operation. Alternatively, annealing is achieved by passing thetube through one or more electrical coils which inductively heat thetube to the desired annealing temperature before the tubing is cut tolength. Following this, the tube-is quenched and passed on to be cut orcoiled in separate stages.

Several drawback exist in the manufacture of tubing as outlined above,for which neither the tube manufacturing nor related manufacturing artssupply satisfactory solutions. For example, the inductive heatingapparatus for small diameter tubing is quite expensive and requires acertain skill to operate and maintain. It thus is ill-suited for use bythe smaller tube producers. Another problem is that the above-describedprocesses do not readily lend themselves to the low-cost continuousproduction of annealed tubing in one fully automatic operation, from thestrip reel to the final coiling of the annealed tubing for shipment.This, too, bears heavily on the economics of smaller operations.

; Accordingly, one broad object of the invention is to reduce the costof manufacturing annealed tubing.

" Another object of the invention is to produce annealed tubing fromstrip to a finished coiled product in one continuous operation.

Another object of the invention is to obviate the need for inductionheating apparatus in the tube making process.

A further object of the invention is to maintain or improve the materialquality of annealed tubing.

A specific object of the invention is to produce stainless steelbeverage tubing faster and at lower cost than heretofore possible.

SUMMARY OF THE INVENTION These objects are achieved in accordance withthe inventive process, broadly, by several new and interrelated stepsincluding the electrical resistance heating of the tube, a quenchingwhich the advancing tube undergoes prior to contacting the secondelectrical brush, feeding of the annealed tube directly into acontinuous coiler, and careful balancing of the advancing forces uponthe tube to assure an unwarped and smooth end product.

The practice of the inventive process is greatly facilitated by certainitems of apparatus, hereinbelow to be described in detail, which arenoteworthy for their simplicity and low cost. In the electricalresistance heating stage, for example, the tube is frictionallycontacted on opposite sides by two sets of stationary brushes, one setlocated at the hot end and the other set at the cold end. Each brush setmay comprise a pair of spring-loaded graphite blocks; or moreadvantageously, two thick spring-loaded graphite discs which impinge thetube from opposite sides and which are each rotatable to presentdifferent sectors of their periphery to the tube. The harsher wearexperienced at the cold end owing to the greater abrasiveness of thetube surface after quenching thus is compensated for without need forfrequent brush replacement.

In the heating stage the tube is advanced through a series ofheat-impervious elements which are more closely spaced at the hot end tocounteract with greater force any tendency the hot tube may have tobend. These elements advantageously are asbestos blocks with guide holeswhose alignment helps define the prescribed straight-line path for thetube. Further safeguard against tube buckling is achieved by the driverollers of the continuous coiler located at the far end of the processline whereby the coiler maintains a slight tension in the heated sectionto prevent buckling.

The quenching step is achieved by feeding the tube through a section ofpipe into which a coolant is being constantly forced through two ringsof perforations near the respective ends of the pipe. The latter, inturn, is enveloped by a larger diameter pipe which serves as a reservoirfor the coolant. The radial flow of the cooling water around thecircumference of the hot tube insures uniform cooling which is necessaryto maintain straightness in the annealed tube. The water, afterimpinging the tube, runs out both ends of the pipe.

In practising the inventive process with the specific apparatusdisclosed below, factors such as the size of tubing, the speed ofadvance, the physical distance between contact brushes, the temperaturegradient and range within the heating stage and other related parametersmust be taken into account in achieving an optimum operation. The moresignificant relationships and the preferred combinations are set outbelow.

A greater understanding of these and other objects, features andadvantages of the invention will be gained from the detailed descriptionto follow of an illustrative embodiment thereof.

DESCRIPTION OF THE DRAWING FIG. 1 is a schematic flow diagramillustrating apparatus which practises the invention;

FIG. 2 is a front view of the brush configuration;

FIG. 3 is a frontal perspective view of an enclosure for the heatingstage;

FIG. 4 is a sectional side view of the quenching apparatus;

FIG. 5 is a sectional side view of a further enclosure for the heatingstage;

FIG. 6 is a perspective view of the continuous coiling apparatus; and

FIG. 7 is a table showing typical process parameter relationships.

3 DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT The invention isillustrated below in its application to the manufacture of so-calledbeverage tubing which typically is stainless steel tube with an outsidediameter of A to inches and a wall thickness of about .020 inch,

and which must be highly pliable. It is broadly applicable,

however, to any small diameter stainless steel tubing, high nickelalloy, or other ferrous alloy tubing that will not harden under waterquench.

FIG. 1 illustrates schematically the overall practice of my inventiveprocess. Stainless steel strip, designated 1, is fed from a coil 2through a conventional tube rolling mill 3 which may consist of one ormore roller pairs such as 4 and 5, for example. These form the basictube shape and also advance the formed tube 6 through the followingstages. The tube seam is joined in a welding feature 7 which, forexample, may be a tungsten inert gas (TIG) arc welding unit 8 suppliedby a source 9.

Pursuant to one facet of the invention, the tube is next directedthrough a first pair of opposed, solid graphite brushes 10, 11. Theseare the above-mentioned blocks or discs and are spring-loaded onto thetube to establish equal contact forces. Brushes 10, 11 are connected byconductor 12 to a high power current source 13, the latteradvantageously being a constant potential welder capable of supplying200 to 500 amperes at a constant voltage of from 2050 volts selected inaccordance with the tube size. The second electrical contact withadvancing tube 6 is with graphite disc brushes 14, 15, the constructionof which is illustrated in more detail in FIG. 2 and will be describedshortly. Brushes 14, 15 are connected by conductor 16 to current source13, which completes a resistive circuit including the portion ofadvancing tube 6 lying between brushes 10, 11 and brushes 14, 15.

In advancing between the two sets of brushes, tube 6 passes through aseries of aligned holes 18 in asbestos blocks 17, as seen in FIGS. 1 and3. Block 17 are about /2 inch thick and are rigidly fastened to afixture such as 19, with the holes 18 aligned along axis 20 whichcoincides with the path of advance of tube 6. Holes 18 are slightlylarger in diameter than the outside diameter of tube 6, the clearancebeing about inch. The tendency of the tube 6 to buckle while beingsimultaneously advanced and heated thus is counteracted, particularly atthe hot end where the spacing of blocks 17 is about half the spacing asoccurs at the cold end.

At a point in'the tubes advance which is reached just prior to the coldbrushes 14, 15, the quenching step is accomplished advantageously withthe quenching device shown in FIG. 4 and designated 21. Quencher 21consists of an inner cylinder 22, through which the smaller diameteradvancing tube 6 passes, and an outer cylinder 23 enveloping cylinder 22and forming a coolant reservoir 24 surrounding cylinder 22. Two rings25, 26 of perforations through cylinder 22 occur about one-third andtwothirds, respectively, along its length. These serve as jets throughwhich coolant is forced from inlet 27 and reservoir 24 into the volumebetween cylinder 22 and tube 6. The coolant, advantageously water, flowsfrom hole rings 25, 26 in a series of jets which radially impinge on theouter surface of tube 6. This action coupled with the complete immersionof tube 6 in the coolant promotes a highly uniform cooling essential toprevent warping of the tube in the cooling step.

The graphite disc brushes 14, 15 of FIG. 2 are disposed adjacentquencher 21. Each comprises a solid graphite disc about three inches indiameter and one inch thick, rotatably mounted from a central threadedrod 29.Bus bars 30, 31 and support arms 32, 33 are secured to therespective rods 29 as with washer nuts 34. Arms 32, 33 are pivoted atfixed points 35, 36, respectively, so that a conventional adjustabletension mechanism designated 37 can be employed with each brush toadjust the force with which it contacts the tube 6. For even heating, itis desirable not only that two brushes be oppositely situated at eachcontact point, but also that these brushes apply equal force to the tube6. When the brushes 14, 15 wear down from the abrading efiect of tube 6,new brush surfaces-in effect, new brushes-are readily available merelyby rotating each brush 14, 15 in turn to a new position. The brushconfiguration illustrated in brushes 14, 15 advantageously may also beemployed with brushes 10, 11.

Serving to keep tube 6 aligned between brushes 14, 15 and coiler 38 is aroller pair 39 which, advantageously, is made of phenolic resin toelectrically insulate the drive mechanism from the tube 6. Roller pair39 optionally is a drive roller which applies a pulling force to tube 6to help prevent buckling of the hot section when necessary, and to aidin feeding the tube onto the run-out table 41 shown in FIG. 1.Alternatively, when a continuous coiler is used, the drive roller of thecoiler may be relied on to help prevent buckling, as will be explainedlater.

The annealed tube can be collected continuously in linear sections, ifdesired, as on the run-out table 41. Here, an electric saw such as 42 isa useful expedient in cutting the tube in straight lengths. Moreadvantageously, however, the tube 6 is formed continuously into coils ofa selected diameter with the coiling apparatus 38 illustrated in FIGS. 1and 6. Coiler 38 consists of a drive roller 40 and two idler rollers 40aand 40b mounted in a.

fixture such as 50 which maintains the rollers in axial alignment withthe advancing tube 6.

Roller 40 applies a pulling force or tension to the tube 6 which issufficiently large to effect the desired coiling. This force, however,must be less than that which would cause the elastic limit of the tubesheated portion to be exceeded. To ensure that result, the power derivedfrom drive roller motor 51 is applied to roller 40 through atorque-limiting clutch 52 whose output torque is adjusted and maintainedat a value less than that which would cause the tube 6 to stretchpermanently.

The coiled tube is collected on a mandril 53 associated with roller 40,coiling being aided by the guides 54 and 55.

The process as so far described involves open annealing in which thetube 6, while being heated, is exposed to the atmosphere. Inconsequence, the tube surface occasionally develops a scale which forbeverage tube and many other applications must later be removed, asthrough pickling. The scaling can be avoided, however, by a brightannealing step in which throughout the heating stage, pursuant toanother aspect of the invention, the advancing tube is protected by aninert gas such as nitrogen or dissociated ammonia.

FIG. 3 illustrates schematically the practice of bright annealing withthe present process. A heat-impervious envelope 43 made of acement-asbestos compound, for example, is disposed around the entireheating stage. The tube 6 enters at port 44, seen in FIG. 1, which issituated beyond the brushes 10, 11, but prior to where scaleforming heathas developed. Then tube 6 exits at port 45 which, for example, may beadjacent the quencher 21. Gas intake and exhaust manifolds 46, 47 withassociated circulating equipment (not shown) service the envelope 43.

Alternatively, the gas container may be composed of lengths of quartzcylinder 48, shown in FIG. 5 as spanning between blocks 17. The inertgas can be circulated in and out of each individual quartz cylinder 48;or, since each quartz cylinders inside diameter is greater than thediameter of holes 18 in blocks 17, the inert gas can be flowed axially.

The tube 6, if stainless steel, must be heated in the present processfrom room temperature to within the range of 1800-2400 degrees F.,typically approximately 2100 degrees F. for proper annealing. The netincrease of tube temperature is proportional to the PR factor of theresistive circuit and to the time required for a given point on the tubeto travel between the two brush sets 10, 11 and 14, 15. The latter inturn is related to the speed of advance of the tube. Another parameteris the distance between brushes which can vary from 3 to 10 feet. Up toa point, higher speeds of advance can be accommodated by increasedcurrents applied through the brushes. Practically, however, speed ofadvance is limited by the upper limits of the speeds of welding. FIG. 7is a table which shows the applied current requirements and otherparameters for two specific tube sizes at their respective Weld speedsto realize final annealing temperatures of 2100 2150 F.

In summary, an improved process is described for the continuousproduction of tubing, particularly stainless steel beverage tubing.Numerous variations on the described process and apparatus will occur topersons versed in the art and all such variations are expressly reservedwithin the legitimate scope of the claims to follow which characterizethe invention.

What is claimed is:

1. A process for continuous manufacture of small diameter annealedstainless steel tubing, comprising the steps of forming a welded seamedstainless steel tube, advancing the welded tube between first and secondspacedapart and current-carrying pairs of opposed graphite brushesmounted about a central rod,

contacting said tube between said opposed brushes by biasing the rods ofeach brush pair together a preselected amount, and

quenching the heated tube prior to its reaching said second brush pairby advancing same through a circulating coolant contained in anopen-ended chamber and within said chamber feeding a plurality ofcoolant and streams radially and uniformally upon said tube surface.

2. The process pursuant to claim 1, wherein said brushes are graphitediscs each disc rotatably mounted on a respective said rod, and each rodbeing aligned normal to the path of tube advance.

6 3. The process pursuant to claim 2, wherein said rods mounting theopposing said discs are connected to first and second pivotally mountedarms, and wherein said contacting step comprises spring-biasing saidarms together.

4. The process pursuant to claim 3, wherein said quenching stepcomprises immersing the heated tube in a coolant contained in anopen-ended cylinder and therein, interiorly of each said open end,directing first and second sets of coolant streams radially anduniformly around said tube.

5. The process pursuant to claim 4, comprising the further step ofenveloping the tubes heated portion in a heat-impervious quartz envelopfilled with a circulating inert gas.

6. The process pursuant to claim 2, comprising the further step ofexposing said advancing tube to new electrical contacting surfaces byrotating said graphic discs to unused portions thereof while adjustingsaid spring bias between said arms to a new preselected value.

References Cited UNITED STATES PATENTS 1,285,887 11/1918 Alexander et al148-154 1,355,521 10/1920 Alexander et a1. 148-150 1,570,815 l/1926Wylie 148-154 2,240,019 4/1941 Quarnstrom 148-127 2,748,039 5/ 1956Adams et a1 148-12.4

2,930,724 3/1960 Rudd 148150 L. DEWAYNE RUTLEDGE, Primary Examiner W. W.STALLARD, Assistant Examiner US. 01. X.R.

